Early experience is associated with the development of categorical representations for facial expressions of emotion

Abstract

A fundamental issue in human development concerns how the young infant's ability to recognize emotional signals is acquired through both biological programming and learning factors. This issue is extremely difficult to investigate because of the variety of sensory experiences to which humans are exposed immediately after birth. We examined the effects of emotional experience on emotion recognition by studying abused children, whose experiences violated cultural standards of care. We found that the aberrant social experience of abuse was associated with a change in children's perceptual preferences and also altered the discriminative abilities that influence how children categorize angry facial expressions. This study suggests that affective experiences can influence perceptual representations of basic emotions.

Figure 1

The stimuli. Children categorized randomly generated “morphs” from blends of four prototypes. Morphed images were created to lie between prototypes of happiness and fearfulness, happiness and sadness, anger and fearfulness, and anger and sadness. These four continua each contained 11 male and 11 female images, of which the end positions were unmorphed prototypes of each emotion. The images each differed by 10% in pixel intensities. The middle face in each continua was a 50% blend of each emotion pair. (Adapted from ref. .)

Figure 2

Results from the emotion identification task for each emotion pair. The ordinate refers to the proportion of trials in which responses matched the identity of the second emotion in the pair relative to the first emotion in the pair (e.g., for the happy–fear pair, signal strength 1 = 90% happy/10% fear whereas signal strength 9 = 10% happy/90% fear). Data for controls are plotted in solid lines and data for abused children are dashed lines. The horizontal dashed line at P = 0.50 is plotted to help identify the threshold for each group. Data for all four emotion continua show a clear change in identity judgments as a function of changes in stimulus intensity. However, abused children overidentified anger relative to fear and sadness.

Figure 3

Results from the emotion discrimination task for each emotion pair. Discrimination performance for the four emotion continua are plotted as proportion correct for sequential pairs of faces along each continuum. Chance performance (0.5) indicates that children had difficulty discriminating between the two sample stimuli. As can be seen, both groups of children showed discrimination peaks for morph pairs in the center of the continua. In all four conditions, discrimination scores were higher for face pairs at the predicted peaks than for pairs near the prototypes. Average discrimination scores for the control children are plotted in solid lines and data for abused children are dashed lines. For controls, peak discrimination scores were near the midpoint of each continuum. Perceptual category boundaries for abused children differed from controls only in continua that involved angry facial expressions. The shift in the abused children's peak discrimination scores relative to controls reflects broader perceptual categorization of anger relative to fear and sadness, respectively.